1. Field of the Invention
The present invention relates to a technical field of flaw detection and preventive maintenance by using an ultrasonic, preferably, laser, maintenance apparatus, wherein both laser nondestructive testing and laser prevention maintenance can be carried out, and particularly relates to an ultrasonic, i.e., laser-based (or merely, laser), maintenance apparatus capable of carrying out flaw testing and prevention maintenance without interchanging devices. The present invention also relates to a surface testing or inspecting, or processing technology utilizing laser such as laser-ultrasonics, which are related to the laser maintenance technology mentioned above.
2. Related Art
One way of ensuring continuous integrity of tubular structures in nuclear reactors is to nondestructively inspect (test) and measure whether there is no initiation of cracks in the structure or no material deterioration thereof and to employ reformation/processing for previously preventing cracking or deterioration of the structure.
In the following, description will be made regarding a bottom-mounted instrumentation tube which is a representative tubular structure in a nuclear reactor.
A bottom-mounted instrumentation tube is a guide tube for guiding, from the outside of the rector to the inside of the reactor, a sensor for measuring neutron flux at a portion near the nuclear reactor core of a pressurized water reactor, and penetrates the bottom of the reactor vessel to which it is welded. Neutron flux of the core is a parameter directly indicating the operating state of the nuclear reactor, and it is important to secure the integrity of bottom-mounted instrumentation tubes dealing with this measurement in the view point of safe operation of the plant.
Nondestructive testing devices for bottom-mounted instrumentation tubes have been proposed in Japanese Utility Model Registration No. 2590283 as shown in FIGS. 74 and 75. This device is a nondestructive testing device 3, capable of being raised and lowered, for testing bottom-mounted instrumentation tubes 2 positioned on the based within a nuclear reactor vessel 1 and has a slender tubular main body 4. Inside this main body of the nondestructive testing device 3 for bottom-mounted instrumentation tubes 2 are provided a guide device 6 having a test sensor 5 for testing the bottom-mounted instrumentation tubes at the tip thereof, a sensor insertion/extracting device 7 for inserting and extracting the test sensor 5 to and from the bottom-mounted instrumentation tubes, and a turning device 8 for turning the test sensor 5 in the bottom-mounted instrumentation tubes, and further, has a clamping device 9 for the bottom-mounted instrumentation tubes 2 at the top end of the main body 4.
On the other hand, laser technology can be used for testing/measuring material within nuclear reactors, such as detecting cracks in structures, measurement of crack size, stress measurement, material composition measurement, distance measurement, vibration measurement, shape measurement, temperature measurement, and so forth, or reforming/processing material within nuclear reactors, such as stress improvement of the material surface, solution treatment, cladding, removal of adhered matter, polishing, crack removal, crack sealing, welding, cutting, and so on, by using features thereof such as high energy density, peak power, coherence, coherent rectilinear propagation, and the like (e.g., Sano et al. “Underwater Maintenance Technology Using Laser for Nuclear Reactors”, Welding Technology May 2005, P 78-82 (2005)”).
In principle, such laser techniques are effectively utilized in cases wherein it is difficult to access to the materials, such as at high temperatures, at high positions, in high-dose radiation fields, at portions with complex shapes, and so on, or at portions where access is poor and remote non-contact techniques are required. There shows application can be effectively realized at portions where it is difficult to spatially send laser beams to the object portion, such as in narrow portions, on the inner side of shielding objects, on the inner face of piping by using optical fiber technology (Yoda et al.: “Transfer of 20 MW Laser Pulses by Optical Fiber and Applications Thereof” Laser Research Vol. 28, No. 5, P. 309-313 (2000)).
Particularly, a nondestructive test technique using laser technology is laser ultrasonics. This laser technology involves generating ultrasonic waves using distortion generated at the time of pulse laser beams being irradiated upon a structure material, and measuring the ultrasonic waves as vibrations signals using the interference effect of reception laser beams irradiated on a different point of the same structure material, and is known by way of, e.g., “Yamawaki: “Laser Ultrasonics and Non-Contact Material Evaluation”, Welding Society Journal Vol. 64, No. 2, P. 104-108 (1995)”. Ultrasonic waves generated and detected or received in this way can be used for various types of crack detection and material measurement for structures, in the same way as with ultrasonic waves generated and received with normal contact type devices.
Furthermore, as for a method for detecting flaws by using laser ultrasonics, a surface test device disclosed in Japanese Unexamined patent application Publication P 3735650 is already known. The surface test device disclosed in this publication relates to technology enabling a method for finding cracks in a structure material which is the subject of measurement, from reflection echoes of generated ultrasonic waves reflected off of cracks in the structure material, or irradiating laser so as to pin a crack found in the structure material between the generation and detection or reception position of the ultrasound, thereby measuring the depth of the crack from the generated ultrasonic propagation properties.
As for a nondestructive test technique of tubular structures within a reactor using laser ultrasonics, the laser irradiation device in Japanese Unexamined patent application Publication No. 2005-40809 is known. As shown in FIG. 76, two laser beams of ultrasonic wave generation laser beam (hereafter referred to as generation laser beam L1) and ultrasonic wave reception laser beam (hereafter referred to as detection or reception laser beam L2) are irradiated on a tubular structure which is the object of testing, and cracks in the subject part are detected using generated ultrasonic signals.
As described with Japanese Utility Model Registration No. 2590283, nondestructive testing devices for bottom-mounted instrumentation tubes are capable of readily realizing nondestructive tests of bottom-mounted instrumentation tubes using a test sensor of a known structure.
However, there is a case wherein, even in the event that no cracks are found in the structure material in the nondestructive test of the bottom-mounted instrumentation tubes, preventive maintenance may be desired for preventing cracks from initiating in the structure material in the future. For example, applying laser technology to preventive maintenance such as improving stress at the material surface of the structure material, is becoming very commonplace (laser peening technology), however, with the nondestructive testing device for bottom-mounted instrumentation tubes using the test sensor with the known structure, a laser maintenance apparatus must be prepared separately from the nondestructive testing device, and the devices must be exchanged each time test work or maintenance work is performed. Exchanging the nondestructive testing device and the laser maintenance apparatus for each task extends the work time in the perspective of the overall task from testing to preventive maintenance, causing the problem of increased costs.
On the other hand, with regard to laser ultrasonic flaw detection devices, while proposals have been made regarding the feasible base technology of using the basic device configuration and flaw detection method, for flaw detection testing of the inner cylinder face of bottom-mounted instrumentation tubes, no proposal has been made regarding an overall system of a nondestructive testing device for bottom-mounted instrumentation tubes combined with preventing maintenance using laser.
Furthermore, the present invention concerns with a laser irradiation device provided for the laser maintenance apparatus mentioned above.
That is, recently, the importance has increased for preventive maintenance technology which prevents premature deterioration of equipment or construction materials of, for example, a reactor construction in a nuclear power plant during a provision period, or in the event that deterioration occurs, maintenance technology such as repairs, maintenance, and prevention of advancing deterioration will be performed.
An optical fiber technology can also be effectively used even where it is difficult to spatially send laser beams to the object portion, such as in narrow portions, on the inner side of shielding objects, on the inner face of piping and so forth.
The surface testing technology uses the laser ultrasonic technology, in which ultrasonic waves are generated by using the distortion of an elastic region which occurs when a pulse laser light is irradiated on a material, and also detects the ultrasonic waves as an oscillating signal, using coherence effect of a reception laser light which is irradiated on the material, and for example is disclosed in the above mentioned publication.
According to this technology, the generated and detected ultrasonic waves can be used for various crack testing or material characterizations, similar to the ultrasonic waves sent or received with a normal contact-type element.
As shown in FIG. 76, with this technology an irradiation head formed with an optical system container, optical fiber, and so forth, is inserted into the cylinder portion of a narrow tube which is the test object, and the generation laser light (laser light for exciting ultrasonic waves) and the reception laser light (laser light for detecting ultrasonic waves) are both in the same direction of the cylinder as to the inner surface of the cylinder, and also toward the axis direction of the cylinder and are irradiated with positions shifted.
The generation laser light L1 excites ultrasonic waves at the sending point E, as shown in FIG. 77. The direct surface wave 104a which arrives at the detecting point R (irradiation position of the detection laser light L2) in a short propagation time detects a crack occurring in the circumference direction as to the axis direction of the cylinder CY.
The orbiting surface wave 104b which orbits the cylinder CY with a long propagation time and arrives at the detecting point R detects a crack occurring in the axis direction of the cylinder CY.
In the case that the test object with a crack is an inner surface of a cylinder as described above, there are several problems such as noise and crack depth measurement.
In other words, when the crack in the test object is on the inner surface of a cylinder, the space is relatively closed, and therefore, other mode ultrasonic signals such as shock waves from the generation laser light L1 is mixed as noise. Furthermore, in the case of measuring crack depth, the two laser lights which are the generation laser light L1 and the detection laser light L2 must be irradiated so as to sandwich the crack. However, if the positions for generation and detection or reception are only for irradiating from a distance in the same direction, as has been the case conventionally, the crack initiated in the axis direction of the test object cannot be sandwiched, and measuring the depth of the crack has been impossible.
Further, with the form of the irradiation head which contains the optical elements internally, depending on the form of the irradiation head, if the inner surface of the cylinder which is the test object has minute curved portions, the work of inserting into and removing from the cylinder which is the test object of the irradiation head becomes inefficient.
The present invention described above further concerns with a laser ultrasonic inspecting device for irradiating the laser to a test object without contact, and generating an ultrasonic wave, and a system including the inspecting device.
Heretofore, as for a flaw-inspecting method of a test object using an ultrasonic wave, the ultrasonic flaw detection method shown in FIG. 78 has been known. With this conventional method, first, a generation-side surface-wave probe 203a including a piezoelectric device is brought into contact with a test object 201 via a generation-side couplant 202a. In this state, an electric signal is applied to the generation-side surface-wave probe 203a from a transmitter 204, an ultrasonic wave is generated to the test object 201 from the surface-wave probe 203a, and a surface wave 205 is generated.
Then, the surface wave 205 is propagated over the surface of the test object 201 and reaches a reception-side surface-wave probe 203b including a piezoelectric device via a reception-side couplant 202b. This arriving signal is received at the reception-side surface-wave probe 203b and is converted into an electric signal by the piezoelectric device to be inputted to a flaw-detecting unit 206. The generation signal from the transmitter 204 is also inputted to this flaw-detecting unit 206, and the difference Δt between the generation time of the generation signal and the reception time of the reception signal, i.e., the time when the surface wave 205 is propagated over the surface of the test object 201 is measured.
When assuming that an interval L between the generation-side and reception-side surface-wave probes 203a and 203b and a sound velocity vs of the surface wave 205 are known, these have the relation that L=vs·Δt. Herein, assuming that the surface of the test object 201 includes a flaw 207 with an opening, which can be ignored, of a depth D, a part 205a of the surface wave 205 is steered around the flawed portion, and consequently, propagation time ΔtD is longer than the propagation time Δt in the case of no flaw.
Accordingly, upon measuring this propagation time ΔtD, the presence of the flaw 207 can be detected from comparison between propagation time L/vs to be measured essentially and the ΔtD, and also the depth D of the flaw can be calculated from the relation of D=(vs·ΔtD−L)/2.
FIG. 79 illustrates a conventional method of surface inspection using an ultrasonic wave. This method is for receiving flawed waves 208a and 208b at the opening end portion and the bottom portion of the flaw 207 based on the surface wave 205 generated to the test object 201 via the couplant 202a from the surface-wave probe 203 for both generation and reception by the surface-wave probe 203 again. With this method, arrival time Δta to the surface-wave probe 203 of the flawed wave 208a and arrival time Δtb to the surface-wave probe 203 of the flawed wave 208b have the relation that 2D=vs·(Δta−Δtb), the depth D of the flaw can be obtained by measuring Δta and Δtb at the flaw-detecting unit 206.
On the other hand, in recent years, a method for substituting with generation/reception of the surface wave 205 using laser light without using the surface-wave probe 203 and the couplant 202 has been proposed. This non-contact surface-wave generation method using laser light is for utilizing a phenomenon in which upon laser light having short pulse high energy being irradiated to a certain test object, thermal stress or evaporation (ablation) compressive force due to absorption of laser energy is generated near the laser light irradiation point, and the distortion due to the affect becomes a surface wave to propagate within the object.
Furthermore, another non-contact surface-wave detection method using laser light is a method for measuring fine vibration which the surface wave excites on the test object surface based on the variation (deflection) of the direction of movement of laser light, the phase modulation of the reflected light, the amount of frequency transition and the like by irradiating laser light to the test object 201 and receiving the reflected light. The above prior technology is disclosed, for example, in J. D. Aussel (“Generation Acoustic Waves by Laser: Theoretical and Experimental Study of the Emission Study of the Emission Source,” Ultrasonics, vol. 24 (1988), 246-255 or C. Chenu (“Defect Detection by Surface Acoustic Waves Generated by a Multiple Beam Laser,” Proc. of IEEE Ultrasonics Symposium (1995), 821-824)
However, with the above conventional ultrasonic flaw-inspection method, it is necessary to apply the couplants at the time of installing the surface-wave probes 203, 203a, and 203b in the test object, which leads to increase of processes of operation. Further, in the case in which the test object is small, or in the case in which the test object is in a narrow portion, it is difficult to install the surface-wave probes.
Moreover, the conventional non-contact flaw-inspection method using laser light provides a problem wherein the data obtaining time for obtaining more detailed data and inspecting a flaw improving resolution becomes huge. Accordingly, there poses a problem in which the capacity of a recording medium for recording obtained data and the flawed portion detection analysis time increase, and there also causes complex work for extracting necessary portions alone from the large quantity of data.
The present invention also includes a laser ultrasonic reception (detection) device related to the laser maintenance apparatus mentioned above, and more specifically, a laser ultrasonic reception device having monitoring functions of device condition, and optimizing functions of the device condition, for performing flaw detecting operations with a high degree of accuracy over a long period of time in a stable state.
Ultrasonic technology is an extremely effective means for detecting cracks or discontinuity occurring on a material surface or internal defects, or for performing material-characterization. With normal detecting operations, the ultrasonic waves is received by placing in contact a receiving element such as a piezoelectric element with a generation medium of the ultrasonic wave, but this can be substituted by using laser light and a receiving (detecting) optical system such as disclosed in Monchalin, J.-P., et al., “Optical detection of ultrasonic,” IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 33, 1986, pp. 485-499.
An ultrasonic reception method with laser light is in principle non-contact. The application is expected in cases wherein the measurement subject is in a high temperature state, or is placed in a high location, or is placed in a high radiation area, or is very small and in a complicated shape so that contact with testing equipment is difficult, or in industrial technological fields wherein the ability to approach in close proximity is poor and a remote non-contact measurement method is required.
The ultrasonic receiving technology by using laser is a technology in which an oscillating laser light with sufficiently longer pulses is irradiated on the receiving point compared to the generating time of ultrasonic waves or continuous oscillation, and the surface displacement of the receiving point induced by the ultrasonic waves is detected by using direct advancement or coherence, or the oscillating speed thereof such as disclosed in Choquet, M., et al., “Laser-ultrasonic inspection of the composite structure of an aircraft in a maintenance hanger,” Review of Progress in Quantitative Nondestructive Evaluation, vol. 14, 1995, pp. 545-552.
As an optical system to use for the laser ultrasonic detection or reception method, a Michelson interference method, a Mach-Zehnder interference method, the Fabry-Perot method, a two-wave mixing method with a phase conjugation element, and a knife-edge method have been proposed such as disclosed in Yamawaki: “Laser Ultrasonics and Non-Contact Material Evaluation” Japan Welding Society Journal Vol. 64, No. 2, P 104-P 108 (1995). However, the method with which industrial applicability is particularly expected is the Fabry-Perot method.
Here, a typical conventional laser ultrasonic reception or detection method and device in which a pulse laser light and the Fabry-Perot method are combined will be described. FIG. 80 is a block diagram illustrating a configuration of a representative conventional laser ultrasonic reception device.
In FIG. 80, an ultrasonic signal US based on an arbitrary generating process or generating process arrives at an arbitrary point P on the surface of a measurement subject TP, and oscillation occurs at that portion. Now, a detection pulse laser light source PDL is appropriately synchronous with the ultrasonic signal US and emits the pulse laser light IL.
The seed laser light oscillated from the seed laser 401 which is set within the detection pulse laser light source PDL is injected into an optical amplifier 402 (MOPA: Master Oscillator Pulsed Amplifier) via a light isolator 405a and total reflection mirrors M1 and M2, and output is amplified in pulses. Herein, as the seed laser 401, a continuously oscillating Nd-YAG laser light source is used, which has a frequency stabilizing function with an output of approximately 10 mW-1 W. MOPA is to excite the optical amplification medium with a flash lamp which is driven by a power source 403 or a laser diode and is cooled with the coolant water W which circulates from the coolant water inlet Win to the coolant water outlet Wout.
The detection pulse laser light IL after amplification is injected into a first optical fiber 404 with a collimator lens L1, and is irradiated on the measurement point P on the measurement subject TP by a first pair of lenses L2 which is set within the irradiation head H. Here, when the reflected light which is reflected by the end face of each optical elements is injected in the seed laser 401 or the optical amplifier 402, optical noise is generated, and therefore optical isolators 405a and 405b may be placed in a position where reflective light can be prevented from mixing in to the seed laser 401 or the optical amplifier 402. Furthermore, an optical attenuator 406 may also be set for adjusting the light output which is irradiated on the measurement subject TP.
As shown in FIG. 81, the irradiated laser light L1 receives modulation to the optical frequency thereof only ±□Vd by the surface oscillation occurring to the ultrasonic signal US (Doppler shift), a portion of the scattered components thereof SL are collected with a second pair of lenses L3 which is set within the irradiation head H, and are injected into the Fabry-Perot interferometer FP via a second optical fiber 407 and a collimator lens L4. Here, a portion of the laser light SL to be injected into the Fabry-Perot interferometer FP is reflected with a partial generating mirror PM1, and the light amount thereof is measured with a reference optical detector 408.
The Fabry-Perot interferometer FP is a resonator comprising two partial reflection mirrors CPM1 and CPM2 which often have conjugated focal points, and the relationship indicated in FIG. 81 is established between the optical frequency of the incident light and the transiting light intensity. The horizontal axis in FIG. 81 indicates the optical frequency v and the vertical axis indicates in the light intensity I of the transiting light. As shown in FIG. 81, the Fabry-Perot interferometer FP has a peak with a specified optical frequency of the transiting optical intensity I thereof, and operates as an optical frequency narrow band filter which rapidly decays before and after the peak. The optical frequency causing the peak can be changed by adjusting the resonator (that is to say, the space between the mirrors CPM1 and CPM2) of the Fabry-Perot interferometer FP. Thus, from the measurement values of the incident light amount of the Fabry-Perot interferometer FP and the transiting light amount, if the mirrors CPM1 and CPM2 are drive-controlled by the piezoelectric element 409 so as to make the frequency where the slope of the curve shown in FIG. 81 is greatest (e.g., point A), to match the frequency of the pulse laser light IL, the optical frequency change ±v d from the ultrasonic signal US can be converted to a relatively great transiting light intensity change ±Id.
By detecting the light signal which has transited the Fabry-Perot interferometer FP with a light detector 410 via a lens 405, and processing with the frequency filter (a high pass filter is often used) 411 according to the ultrasonic frequency US, an electric signal according to the ultrasonic signal US can be obtained. The detected electric signal is appropriately signal-converted, signal-processed, displayed, and recorded with the signal processing device 412. For the light detector 408 or 410, a photodiode (PD), PIN-type photodiode (PIN-PD), or an avalanche photodiode (APD) is often used.
The output signal of the light detector 410 is separated and processed with the frequency filter 413 (often a low pass filter) for observing transiting light amount change and inputted into a piezoelectric element drive control device 414, and is supplied to the control of the resonator as described above.
Further, although the above description has been focused on the transiting light of the Fabry-Perot interferometer FP for simplification, an ultrasonic signal US can also be detected with the reflecting light from the Fabry-Perot interferometer FP by using similar operations as disclosed, for example, in Dewhurst, R. J., et al., “Modeling of confocal Fabry-Perot interferometer for the measurement of ultrasound,” Meas. Sci. Technol. 5 (1994) pp. 655-662.
As shown in FIG. 82, it is known to irradiate the measuring object TP by the reception laser light IL using pair of lenses L6 set in the irradiation head H and optical fiber 415a, and a configuration to collect the scattered components SL on the measured object TP surface is also known. In this case, the scattered light SL which is generated from the measuring object TP side to the Fabry-Perot interferometer FP with the optical fiber 415a is separated from the light path of the reception laser light IL with a beam splitter 416a and is then guided to the Fabry-Perot interferometer FP via a coupling lens L7 and optical fiber 417a. In order to effectively perform the separating of the scattered light SL and ultrasonic reception laser light IL, a separated control with deflection using an optical element for deflecting control such as a wave plate and a polarized beam splitter may be adapted.
Furthermore, the laser ultrasonic detection or reception methods and devices of known technology are established as basic principles and can be sufficiently applied in a controlled environment such as a laboratory environment.
However, in a site environment such as a power plant or manufacturing line, when a conventional laser ultrasonic reception method and device as described above are used for a long time for defective flaw detecting or measurement work with ultrasonic waves, the following adverse effects are caused by position shifting of the optical elements due to temperature changes or oscillation in the device setting environment, and temperature changes of the coolant water used with the device, or time degradation of receiving laser excited by flash lamps used in a laser ultrasonic reception method and device:
(1) output decrease of seed laser light or oscillation abnormality,
(2) output decrease of pulse laser light or occurrence of waveform distortion,
(3) increase in optical fiber coupling loss, and
(4) control unstable or control impossible of the resonator length of a Fabry-Perot interferometer.
In other words, there have been fatal problems such as the flaw detection operation becoming unstable and the flaw detection precision decreasing due to the adverse device states. Moreover, in order to secure a fixed device state over a long period of time, the conditions needed to be adjusted frequently and the operation became complicated and flaw detecting costs increased greatly. In order to enable flaw detection operations at a high degree of precision over a long period of time at a more stable state, it is necessary to monitor the above device state appropriately, and to reset the best conditions as needed.
The present invention also includes an ultrasonic inspecting device and an ultrasonic inspecting method for performing flaw detection using ultrasonic waves, preferably laser, related to the laser maintenance technology mentioned above according to the present invention.
With nondestructive tests using ultrasonic waves in a nuclear power plant, it is important to accurately record the storage date and time of testing data, the place of testing and the testing results. Additionally, in recent years, subjectivity of the test evaluation and the traceability of the test results have increased in importance.
In order to evaluate the overall safety of power plant equipment, a visual test (VT) or an ultrasonic test (UT) is performed as to the testing equipment which is an object for each periodic maintenance. In the event of such maintenance, a person holding certification for each method performs the tests according to the established examination procedures. Particularly with regard to UT, there are qualifications for testing performed based on the international standard ISO 9712 of the International Organization for Standardization (ISO) or the Japanese Society for Nondestructive Inspection standard NDIS 0601, and testers holding these certifications perform testing appropriate for each equipment according to the examination procedures determined in advance.
With UT, in addition to manual testing, recently a method wherein test data is stored with an automatic device, and the tester performs an evaluation, has become common. A report is created from the test results from the test performed by a tester according to the items required to be reported specified in, for example, “JIS Z 3060” after the tester returns to the office.
Now, the specification content of a general nature such as “constructor or manufacturer” or “process or product name”, in addition to items necessary for each testing location such as “test date” or “examination number or code”, “flaw detection range”, “flaw detection data”, and “pass/fail and standards thereof” are included for each testing location by the tester, and after the tester has personally signed the report, the test report is reported and submitted to the test client.
At this time, particularly in the case of storing test data with an automatic device, the stored test data is not analyzed at the site where the test was conducted, and the tester may return to the office, and after performing analysis may create, report, and submit the test report, similar to the procedure for manual testing.
The content to be included in the report may depend on ASME specifications or other specified confirmation function examinations, in addition to “JIS Z 3060” which is based on the testing technique or test object.
With the test method of performing analysis after returning to the office without analyzing the test data at the testing site, much labor is required, such as the tester recording the “flaw detection range” for each test location which is required to be recorded for example, and in the case of creating the test report, the tester including “flaw detection data”, “flaw detection range”, and numerous other items in the report.
Thus, a device has been proposed to store the size of the test object defect along with the “flaw detection location” thereof, for example, refer to Japanese Unexamined patent application Publication No. HEI 6-265372
With the method of storing the size of the test object defect along with the “flaw detection location” thereof, information such as the test results and the “flaw detection location” thereof are automatically stored, as opposed to the “flaw detection location” information and the results thereof being recorded at the test site and later included in the report, and thus the workload on the tester to create the report is significantly lessened.
Furthermore, a method has been proposed to transfer the test data to an analysis computer from the test site using a communication system, for example, as disclosed in Japanese Unexamined patent application Publication No. 2002-296256.
According to the method using a communication system, the tester can make test determinations without going to the test site.
The above publications, however, do not describe the details relating to a recording method of test data, and in the case of recording a large amount of test data, from the perspective of test data traceability, in order to analyze the test data after the test or reviewing the test data several years later, accurate records of the test data is necessary such as testing date and time, the units tested, and flaw detection ranges or the like. In addition, tamper-proofing of the test data or test reports is also necessary.
The present invention still includes an improved technology of surface testing which can measure even a fine flaw depth with high precision without being influenced by noise and is particularly related to the laser maintenance technology according to the present invention.
Many techniques for flaw testing and measurement of material properties of a material surface layer often employ measuring of a surface wave serving as an elastic wave propagating along the surface of a material.
Such a flaw testing is performed by contacting a surface-wave probe to the surface of a test object via an ultrasonic propagation medium to transmit a surface wave, receiving a signal with this probe and determining the presence of a flaw by an echo from a flaw opening portion.
In addition, there is disclosed a technique for measuring a flaw depth by detecting the delay time of signal components passing through a flaw opening portion, and ultrasonic components which reflect or diffract at the end portion of a flaw in, for example, Yugoro Ishi (“New edition non-destructive-testing engineering,” Sanpo Shuppan, 1993, P 242).
On the other hand, a technique of utilizing the properties where a surface wave distributes, installing each of probes for generation and reception at a position sandwiching a flaw, and estimating a flaw depth based on the fluctuation of a surface wave generating a flaw has been also disclosed in, for example, Japanese Unexamined patent application Publication No. HEI 10-213573.
According to the disclosed technology, as shown in FIG. 83, an oscillator 501 for generating a signal having a predetermined frequency f generates the signal, which is then converted into a surface wave by a generation ultrasonic probe 502 and generated to an object TP to be tested.
A surface wave SR propagates the surface of the object TP to be tested, and if a flaw C exists in the object TP, the surface wave SR interacts with the flaw C to become a generation wave ST, and is received at a reception ultrasonic probe 503. This reception signal is received by a receiver 504, processed by a data analyzing device 505, and then, the presence and depth of the flaw C are calculated.
It is to be noted that a probe to be employed for generation and reception is a contact-type probe utilizing piezoelectric effect. In this case, an ultrasonic propagation medium 506 is applied between the object TP to be tested and the generation and reception probes 502 and 503.
This technique is for utilizing that the penetration (flaw) depth of a surface wave varies depending on the frequency f, and estimating a flaw depth by the attenuation ratio for each frequency of the surface wave generated through a flaw of a material surface layer. Specifically, a waveform including several different frequencies f1, f2, and so on through fn is employed as a generation wave, the attenuation ratio α(f) for each frequency of a reception wave generated through a flaw of a material surface layer is obtained on the basis of the reception wave propagated a sound portion, and the depth of the flaw C is calculated according to the attenuation ratio percentage.
Thus, according to the described prior technology, not only the presence of a flaw but also the depth thereof can be obtained by calculating the attenuation ratio of the surface wave for each frequency.
Further, as for a technique for obtaining the depth of a flaw from the frequency components of a generation wave, a technique for identifying the propagation properties of the surface wave has been proposed, for example, as disclosed in Japanese Unexamined patent application Publication P 3735650.
This technique provides two reception ultrasonic probes, detects a surface wave SR entering a flaw at the reception probe near the generation probe, detects a surface wave ST generated through a flaw C at the reception probe far from the generation probe, and obtains the propagation properties at a flawed portion of the surface wave based on these two signals.
For example, with the power spectrum of a surface-wave signal entering a flaw as R(f) and the power spectrum of a surface-wave signal generated the flaw Injected(f), change in the frequency components by the flaw, i.e., a transfer function H(f) is obtained as H(f)=T(f)/R(f).
This identifies the depth of the flaw logically from the response time and cut-off frequency of the propagation function H(f), or with reference to the results of a calibration test which has been obtained beforehand.
Further, it has been proposed that the detection of a flaw, identification of the position thereof, and measurement of the flaw depth are performed simultaneously by employing multiple reception ultrasonic probes.
This technique has also disclosed that the same operations can be realized by employing multiple generation ultrasonic probes instead of employing multiple reception ultrasonic probes, and also disclosed that as for a generation and reception method of a surface wave, a laser ultrasonic method and an electromagnetic wave method are employed.
Further, another technique for obtaining the depth of the flaw from the frequency components of a generation wave has been provided in the prior art publication mentioned above.
That is, in the above prior art technology, when the length of the flaw C becoming smaller than the width of a surface wave beam generating the flaw portion, the amount of attenuation of the surface wave receives is influenced by both the depth and length of the flaw, (in the surface wave beam, a part thereof is attenuated by generating the flaw, and detected in a mixture of remaining components which do not transmit the flaw), so that it is difficult to detect them distinctively, which leads in accurate detection of the depth of the flaw.
However, as mentioned above, the power spectrum R(f) of the generation wave generating a sound portion and the power spectrum Tc(f, h) of various generation waves, which have a sufficient length as compared with the width of the surface wave beam, generated through a flaw having a depth h, have been beforehand obtained at a calibration test. In addition, a generation power spectrum T(f, h) generated through a flaw having an unknown length and depth is measured, which is represented, by using a coefficient K, as T(f, h)=K×Tc(f, h)+(1−k)×R(f).
Then, the parameter K regarding the flaw length and the flaw depth h are estimated with a regression calculation.
Still furthermore, another technique for obtaining the depth of a flaw from the frequency components of a generation wave has been disclosed in Japanese Unexamined patent application Publication No. 2001-4599.
This technique employs an ultrasonic wave including multiple frequency components, normalizes the amount of generation of an ultrasonic wave generating a test object, and detects the type and depth of the surface flaw from the frequency distribution pattern of the normalized amount of generation.
The technologies disclosed in the above patent publications are ones to measure the depth of a flaw by focusing attention on the attenuation of the frequency components of a surface wave generated through a flaw, which is effective in that the depth of a flaw can be correctly planned.
However, these technologies involve several problems such as follows. Noise generation is a first problem. With this noise problem, as shown in FIG. 84, when the horizontal axis is taken as a frequency f, and the vertical axis is taken as a power P, when a noise is applied to the true power spectrum shown in a dashed line in FIG. 84, this becomes a jagged parabola line such as shown with a solid line, and a comparatively great measurement error is generated as to the true power spectrum.
Particularly, the prior technologies mentioned above focus attention on the discrete and effective number of frequencies, employs a technique for estimating a flaw depth based on the attenuation ratio α(f) or the generation power T(f, h) in each frequency, and accordingly, influence of noise is great, a measurement error occurs, which has involved some uncertainty about measurement values.
Measurement precision is a second problem. That is, a flaw depth which can be measured depends on the band width of a probe or a transmitter/receiver, or the attenuation properties for each frequency of a material, and accordingly, measurement precision gets worse as to a relatively shallow flaw or a relatively deep flaw.
Such a problem will be described in more detail.
Generally, a surface wave has properties to be localized over a surface layer portion of one wavelength thereof. With a material, of which sound velocity of a surface wave is 2900 m/s, e.g., a stainless steel, the penetration (flaw) depth of the surface wave of each frequency forms a depth diagram markedly varying at frequency of 0.1 MHz through 100 MHz as shown in FIG. 85.
For example, the prior technologies mentioned above have a bandwidth up to 10 MHz and employ an ultrasonic wave having a peak at 6 MHz. Upon plotting this peak frequency 6 MHz in FIG. 85, the penetration depth thereof exhibits 0.5 mm. Accordingly, in the event of measuring a fine flaw depth of 0.5 mm or less, a frequency band becomes a frequency region higher than 6 MHz. Consequently, evaluation is performed with weaker signal power than at the time of evaluating a flaw depth of 0.5 mm or more. This means deterioration of the signal-to-noise ratio (SNR) of a signal to be evaluated, and consequently, for example, between a flaw depth of 0.3 mm or less to be evaluated principally with surface wave components of 10 MHz, and a flaw depth of 0.5 mm or less to be evaluated principally with surface wave components of 6 MHz cause a difference in measurement precision thereof. That is, the finer a flaw is, the poorer the estimation precision of the flaw depth becomes.
Such a problem could be avoided by employing an ultrasonic signal having broad and flat power spectrum distribution from a low frequency to a high frequency band as ultrasonic signal strength to be generated/received.
However, in order to realize the wideband properties using an ultrasonic probe which employs a normal piezoelectric device, a lot of cost needs to be spent. As for a high-frequency band, even if an ultrasonic signal having a wide and flat power spectrum distribution can be oscillated, and the propagation attenuation within a material differs for each frequency, so that the signal strength of a high-frequency region decreases at the time of receiving a signal, and the measurement precision of a fine flaw depth gets worse.
Furthermore, another method for obtaining the depth of a flaw from the frequency components of a generation wave is a method for detecting a surface flaw which is characterized by the technologies such that an ultrasonic wave including multiple frequency components is employed, the amount of generation of the ultrasonic wave generating a body to be inspected is obtained for each frequency, which is then normalized with the amount of generation of the ultrasonic wave generating a sound portion of the body to be inspected obtained for each frequency, and the type and depth of the surface flaw are detected from the frequency distribution pattern of the normalized amount of generation such as disclosed in, for example, Japanese Unexamined patent application Publication No. 2001-4600.
As for another ultrasonic flaw-detecting device, there is proposed a technique for determining the presence of a flaw based on change in attenuation or the generation time ratio of the amplitude of the generation ultrasonic waves of a sound portion having no flaw and flawed portion such, as disclosed in, for example, Japanese Unexamined patent application Publication No. 2000-241397.
However, these conventional techniques provide a problem of deviations occurring in each surface wave to be measured depending on surface state.
That is, when generating an ultrasonic wave to an object to be tested, in the case of a piezoelectric device, there will often case a case in which deviations regarding strength of being pressed to the object to be tested vary for each inspected portion, and the ultrasonic signal level varies.
Further, with the electromagnetic ultrasonic method, the ultrasonic signal level varies for each inspected portion due to the changing in the lift-off with respect to the object to be tested. This causes a problem particularly at the time of performing an in-service component such as the case in which the object to be tested includes a curvature, or by driving precision of the driving mechanism of a probe.
Furthermore, in the laser ultrasonic method, the deviations in surface states cause the deviations in the reception sensitivity and the ultrasonic signal level to be excited.
Generally, these deviations are caused by the deviations of the surface condition for each inspected portion, and the installation position errors of a measuring device, which cause flaw depth measuring error.
Furthermore, the conventional techniques provide a further problem of an error in estimation of a flaw depth by the deviations of the evaluation index values at a sound portion and the deviations of the evaluation index values at a flawed portion occurring when comparing the amount of generation of an ultrasonic wave between the sound portion and the flawed portion to perform determination and sizing of the presence of a flaw.
Still furthermore, many of the conventional techniques shown in the above prior art publications perform comparison with a sound portion at the time of estimating the presence and depth of a flaw, and estimate the presence and depth of a flaw based on the amount of change in amplitudes and frequencies. However, in a real measurement, deviations occur even in multiple data measured at a sound portion, and the deviations thereof are sometimes erroneously taken as the amount of change of a flawed portion.
Although these techniques have the assumption that a sound portion and a flawed portion could be measured with the same sensitivity, as described above, in the event of a piezoelectric device, the deviations regarding the strength to be pressed and the state of being pressed cause measurement error, and the lift-off for the electromagnetic ultrasonic method and the surface state for the laser ultrasonic method cause measurement error. Consequently, it becomes difficult to accurately compare the sound portion and the flawed portion.
A further problem of the conventional techniques resides in the case of accurately measuring the change in the depth of the flaw or the case of scattering, by the material itself, an ultrasonic wave strongly. There may cause a case that the change is not detected only by the amount of change of the generated surface wave. As a result, it sometimes becomes difficult to measure the depth of the flaw.